Salmon makes waves

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Clay Point is the model of salmon farms to come in the Marlborough Sounds, says New Zealand King Salmon chief executive Grant Rosewarne.

On a visit to the Tory Channel farm, Mr Rosewarne says the farm is ideally located in deep water with strong currents which carry away any waste with minimal effects on the Sounds environment.

A state-of-the-art feeding system uses digital cameras to capture the moment when pellets fall below feeding fish so distribution can be cut off. Less than 1 per cent of feed falls to the sea floor. On proposed new farms, a fully automated system will be used.

King Salmon has applied to the Environmental Protection Authority for permission to farm salmon at nine new sites in the Marlborough Sounds.

An assessment of environmental effects report supporting its application says seven of these have been selected for their depth and high-speed currents.

At Clay Point, 600,000 salmon grown from smolt raised in the company's hatcheries take 18 months to reach harvest size, compared with three or four years in the wild, Mr Rosewarne tells the Marlborough Express and Guardians of the Sounds on a visit to the farm last month. The fish are anaesthetised and killed on-site, processed at the company's factories in Nelson, then sold in New Zealand markets and overseas.

"Salmon in the supermarket can be as little as a day old," Mr Rosewarne says.

The fish are fed 1700 to 2000 tonnes of feed a year, he says. Fish meal makes up 10 per cent of protein in feed pellets, but most comes from chicken and also sheep and cattle meat.

Of the pellets eaten by the salmon, 20 per cent ends up as faeces, which is an improvement on past conversion rates, Mr Rosewarne says.

King Salmon is applying to add an initial 19,500 tonnes of fish feed per year to the sea at its proposed farms, gradually increasing to 38,000 tonnes if monitoring confirms standards are being met.

King Salmon general manager Mark Preece says that as part of consent conditions, each year Cawthron Institute scientists test surrounding water. At Clay Point, no extra nitrogen (from faeces) could be detected at the surface boundary of the farm, he says.

Mr Rosewarne points to a woman fishing from a boat moored off a nearby reef, to demonstrate that a short distance from the farm the water is clean and supports fish.

To Pete and Takutai Beech of Guardians of the Sounds, the farm is the marine equivalent of a pig farm, intensively feeding its stock in a confined space.

The Beeches fronted up on the Clay Point visit, which Mr Rosewarne acknowledges must have been difficult given their opposition to his company.

"Dairy farmers can't discharge their waste into streams," Mr Beech says. "Letting these farms release waste from 600,000 fish into the sea is a double standard."

It's a parallel Mr Rosewarne rejects.

Unlike cows, cold-blooded fish do not carry bacteria, such as E. coli and salmonella, which affect warm-blooded animals such as people, he says.

In the big picture of the Marlborough Sounds, waste produced by the 600,000 fish at Clay Point is insignificant, Mr Rosewarne says. For whatever reason, the number of wild fish in the Sounds had fallen, so total volumes of fish faeces released must also have dropped.

Mr Beech says unlike mussels, which remove pollution from water, farmed salmon rely on inputs of feed and chemicals and release faeces and other contaminants into the sea.

Pollution by raised nitrogen levels causes oxygen depletion which creates the marine equivalent of deserts under farms, he says.

Excessive nitrogen can increase the size and duration of algal blooms, some toxic to fish and also humans who eat affected shellfish, Mr Beech says.

In June 2010, an algae bloom in Queen Charlotte Sound forced King Salmon to move a farm from Ruakaka Bay to Otanerau Bay, and killed fish, Mr Beech says. He suspects waste from the farm washed into the Grove Arm and fed the bloom.

However, Mr Preece is confident the salmon farm did not promote the bloom because the main current flow was not into Grove Arm but out to sea. Water levels there are fairly constant due to fresh water flowing in.

Mr Preece quotes a paper written on the bloom, which says rainfall and sunlight coupled with a high level of nutrients (mostly nitrogen) in the water provided perfect conditions for algae to bloom. The company keeps an eye on blooms in Grove Arm and monitors them for any risk to the farm.

Mr Beech says zinc added to feed and copper anti-fouling used on nets which keep out predators such as seals and sharks build up in sediment below the farm while nitrogen pollution drifts away.

Mr Rosewarne says zinc stops salmon from going blind so is added to feed for animal welfare reasons. However, the company recognises depositing zinc on the seabed is not desirable so has halved the amount in feed and is moving towards forms which worms and bacteria can break down more easily.

Mr Preece says salmon eggs were first brought into New Zealand in 1906 and by fluke did not carry any major salmon diseases. Fish diseases are generally species-specific, so given that the wild salmon in New Zealand waters are also disease-free, a disease outbreak is highly unlikely.

In its environmental assessment, King Salmon concedes New Zealand's enviable disease-free status might not last.

"In the future, if the need arose ... antibiotics, lice treatments or other animal remedies may need to be added to the feed," the report says.

At Clay Point dead fish, called "morts", are regularly pumped from the bottom of the farm and taken away in sealed containers for disposal at the Blenheim landfill. This is at least twice a week, if not daily. Mr Preece explains that farmed fish mortality rates are insignificant compared with wild populations.

"Salmon produce many eggs which, in an uncertain natural environment, have only a slim chance of making it to adulthood," he says. "When you are farming those sorts of animals you end up with a higher mortality rate."

Mr Beech says King Salmon has stated that proposed farms will be kept away from homes and baches "but this turned out to be a lie". One example was Picton fisherman Lawrence Gledhill's property near the proposed Ngamahau farm in Tory Channel.

Mr Rosewarne says the proposed farm's original site was not close to the bach. At the last minute a reef was found forcing a shift to a site out to sea from Mr Gledhill's property, which King Salmon offered to purchase, he says.

In a report supporting the King Salmon application, Nelson-based Cawthron Institute says research in New Zealand and overseas has shown feed and faeces from fish farms can transform well-aerated and species-rich soft sediments under cages into oxygen-depleted zones dominated by just a few species or even devoid of life.

The report says fish farming has failed in areas of the Marlborough Sounds where, unlike Clay Point, flushing is poor or the water is warm. Photos show a white, mat-forming bacteria covering the sea floor below King Salmon farms.

If a farm is removed, in the Marlborough Sounds it takes up to 10 years for the seabed below to fully recover, the report says.

Cawthron says waste products from fish farms can be detected up to two kilometres away, particularly at high-flow sites. Levels are diluted to a point where there is no environmental effect but waste can deposit in places such as blind bays with no current flow.

Cawthron sampling identifies when conditions reach a trigger where oxygen levels are low and hydrogen sulphate gas, smelling like rotten eggs, bubbles up if the seabed is disturbed. At this point, the number of bottom-dwelling worms which feed on farm waste peaks along with the waste-processing ability of the site. If conditions worsen, the worms start to die.

Mr Rosewarne says this trigger point has not been reached at Clay Point, and his company will carefully increase fish numbers.